Quick couplings e.g. for hydraulic conduits, which operate under very high pressures, are earlier known e.g. from SE-C-406.364 and SE-C-410.508. In these designs the male part at one of its free ends is provided with axial slots, which subdivide the end portion into a number of resilient tongues provided with a radial shoulder, which in the interconnected position of the coupling parts cooperates with an annular stop in the female part. At disengagement the male part is pushed axially into the female part, whereby is obtained an interconnection with an axially movable disengagement member and a simultaneous compression of the tongues, thus that the radial shoulder of the tongues may pass the annular stop of the female part and allow the parts to be pulled apart.
It is a drawback at these known quick couplings, that it is not possible to know with absolute certainty that the radial shoulder of the tongues has really caught behind the annular stop.
The reason for this uncertainty is that the disengagement member at the interconnection of the two parts may be situated in such a position, that the resilient tongues slide into the disengagement member and is radially compressed, which means that the shoulder of the locking tongues can not catch behind the annular stop. The seals of the quick coupling and the spring force in the different parts provide that the different parts may be rather fixedly inserted into each other, but when the hydraulic pressure is applied to the coupling the parts will be urged apart, with all the consequences caused by a "burst" hydraulic conduit under high pressure.
The manufacture of these quick couplings is rather complicated and requires high-tensile steel and very fine tolerances, at least in the male part, as the tongues alone must absorb the entire hydraulic pressure load. The tongues can neither be to coarse, as the interconnection shall be carried out manually without bigger efforts.
From U.S. Pat. No. 3,887,222 is known a quick coupling of similar type as that described above, but wherein the locking member is a slotted, resilient locking ring, which is positioned in a groove turned out in the male part. The locking ring can be brought to cooperate with an axially movable disengagement member inside the sleeve-shaped female part, which at the disengagement of the parts exerts a radial pressure on the slotted locking ring, thus that this is compressed and slides under the annular disengagement member. A radial compression of an axially slotted locking ring, which shall be able to absorb considerable compressive stresses axially, via a chamfered end edge requires big force, which makes the coupling considered as very stiff. Also this design suffers from the same drawback as that described above, i.e. that at interconnection of the male and female parts the locking ring may get stuck on the disengagement member, which prevents the locking ring from expanding, thus that no locking of the parts relative to each other is obtained.
A quick coupling intended for domestic use, e.g. as a quick coupling for garden hoses is known from U.S. Pat. No. 3,731,955, and which is equipped with a combined locking and sealing ring of rubber or plastic material having a V- or U-shaped cross-section. The coupling is designed for low pressures, as one inner shank 9 of the cross-sectionally V-shaped locking and sealing ring shall be able to absorb the axial pressure stresses of the coupling. This design is not useful in hydraulic applications where pressures of over 200 bars occur. On one hand the inner shank of the locking ring will be exerted to so big shear forces that the inner shank will be cut off, on the other hand the risk for permanent deformations in the inner shank are so big, that it will become very difficult to disengage the parts. As the locking ring also shall have a sealing function and it shall be possible to position it in the annular recess in the female part, it must be of rather soft material, which in turn means that the sealing and locking ring rather easily may fall out off the recess, when the parts are not interconnected. Disregarded from the sealing function it should of course be possible to design the V-shaped locking ring from a harder material, e.g. spring steel, but it is then in practice impossible to compress it manually, when the parts shall be pushed together.